Many research groups proposed different hydrogen storage materials such as metal hydrides, chemical hydrides (NaBH4, KBH4, LiBH4, etc), metal-organic framework (MOF), nano-structure materials (CNT, GNF, etc), polymer-metal complex compounds, etc. However, these proposed hydrogen storage materials have disadvantages for commercialization as storage materials, for example; 1) poor hydrogen storage capacity that cannot even reach the minimum hydrogen storage rate (6 wt. %) proposed by US DOE (department of energy) for practical use; 2) poor reproducibility of hydrogen storage capacity; 3) requiring tough conditions for hydrogen absorption and desorption; 4) structural disintegration during hydrogen absorption and desorption; and 5) requiring the development of reproduction process.
In the case of the organic-transition metal hydride recently developed and applied for patent by Hanwha Chemical Cooperation R&D Center, it seems to be adequate for commercialization owing to the advanced properties such as 1) improved hydrogen storage capacity with high efficiency, compared with the conventional hydrogen storage material because of Kubas binding between hydrogen and a specific transition metal (Ti, Sc, V, etc); 2) moderate conditions for hydrogen absorption and desorption (absorption: 25° C., 30 atmospheric pressure; desorption: 100° C., 2 atmospheric pressure); and 3) no-structural disintegration during hydrogen absorption and desorption (Korean Patent Application Numbers 10-2007-0090753, 10-2007-0090755, and 10-2008-0020467).
Korean Patent Application No 10-2007-0090753 and Korean Patent Application No 10-2007-0020467 describe methods for preparing organic-transition metal hydride based on hydrodehalogenation (-M-X bond→-M-H bond) using a hydrogen source and a catalyst. However, these methods cannot avoid the problem caused by catalytic poisoning and side-reaction by inorganic hydroxide used as a neutralizing agent. Besides, separation and purification of a produce is not easy and various byproducts are produced by solvent.
To overcome the said problems, Korean Patent Application No 10-2008-0020467 provides a method to produce organic-transition metal aluminum hydride complex by reacting organic transition metal halide and aluminum hydride compound and then to produce organic-transition metal hydride by reacting the produced organic-transition metal-aluminum hydride complex with Lewis base.
However, the Korean Patent Application No 10-2008-0020467 has the following problems.
First, in relation to the reaction step, a target product is produced by 2-step reaction. Thus, this reaction exhibits lower efficiency and takes longer time, compared with 1-step reaction.
Second, in relation to the process of separation and purification of the intermediate (organic-transition metal-aluminum hydride complex) produced from the first reaction step, alcohols used for separation and purification of the intermediate are reacted with the intermediate to produce diverse byproducts.
Third, in relation to the separation and purification of the final product produced from the second reaction step, triethyl amine and butyl lithium used as Lewis base are very well dissolved in a polar or non-polar solvent, so that it is very difficult to separate these compounds from the product completely when they are present as non-reactants.
Therefore, the Korean Patent Application No 10-2008-0020467 is limited in production of organic-transition metal hydride with high yield because of the said problems.